As people's interest in whitening teeth is increased, a number of toothpaste having tooth whitening effect is commercially available. However, even though the toothpaste contains a tooth whitening agent of good performance, it is hard to achieve a significant teeth whitening effect in a short period of time, by brushing teeth for 1 to 3 minutes of contact time between teeth and toothpaste.
Recently, in order to solve the above problems, a number of patent applications related thereto has been filed and tooth whitening products of various formulations have been introduced in the markets.
Among them, for the professional whitening gel, a patient needs to visit a dentist once or twice to examine his exact dental condition and to measure size of teeth. The dentist manufactures a mouth tray fitting teeth of the respective patient based on the examination and measurement. The patient applies a whitening gel to inner walls and a trough of the tray following instructions at home and wears the tray overnight or twice a day for 2 to 4 days in a week. Typically, the above treatment will be completed in 2 to 4 weeks. However, it has disadvantages in that using the tray is not convenient for a patient and when wearing the tray, the patient experiences discomfort feeling. Further, the patient has to pay lots of money to fabricate his own mouth tray. In addition, a peroxide gel at a high concentration loaded in the mouth tray may flow upon teeth and contact with gum, causing irritation or damage of the gum or mouth cavity.
In order to solve these problems, Japanese Patent No. 10,017,448, assigned to Lion Cor. discloses plasters for oral cavity, which comprises a teeth adhesion layer and a supporting layer. A whitening agent which can be used in this patent includes kojic acid and derivatives thereof, ascorbic acid and derivatives thereof, carbamide peroxide and the like but kojic acid and various salts thereof are described as being particularly effective. However, since the above-mentioned whitening agents have a strong acidity, it may cause irritation in an oral cavity due to a low pH. Such agents can provide superior whitening effect at a high acidity. Therefore, it is difficult to obtain a plaster of good whitening effect without irritation.
The kojic acid is widely used in skin care products. However, it has not been proved to have tooth-whitening effect and has not been used as a tooth-whitening agent. In practice, when adding ascorbic acid and derivatives thereof, or carbamide peroxide as a whitening agent respectively to a patch formulation comprising a glass polymer as an adhesive, discoloration and stickiness occurs as time goes by. In particular, when adding carbamide peroxide, severe problems occur in terms of storage as crystal forms at a temperature 40° C.
In addition, the whitening agents mentioned in the patent are usually considered to be unstable. However, the patent does not include a description with regarding to a stabilization of these whitening agents. The above patent seems to be an idea patent, which is formed by combining kojic acid, which is a typical raw material of cosmetic composition for skin whitening, produced by Lion Cor. into a plaster formulation using a common polymer without conducting concrete studies.
Japanese Patent No. 12,281,548, filed on Mar. 16, 1999 and published on May 30, 2000, discloses a tooth whitening kit set. Claim 2 describes a water-insoluble tape, sheet, film, dental tray, mouth tray, mouthpiece, impression pack, pack material, and chewing brushing having a plurality of protrusion on a surface contacting with teeth and prepared by forming upon dental arch. Upon reviewing the specification, the invention is characterized by thinly applying a whitening component in a gel phase on a supporting layer of the above appliances or by immersing the adhesion portion of the above appliances in a solution containing a whitening agent. That is, the appliances claimed in this patent are wet type. When using such type of appliances, the whitening agent may contact with hands or other part of body, causing irritation.
Further, the adhesion portion of water-insoluble tape or sheet is composed of woven or non-woven fabric, for example, rayon, cotton, silk or paper while the supporting layer is composed of water-insoluble film, for example, polyethylene, polypropylene, polyester, etc. Thus, it is not considered that the invention is improved over the Patent No. 10,017,448.
Meanwhile, this invention uses a poly phosphate as a whitening agent, instead of peroxide along with anionic surfactant and low molecular weight alcohol having not more than 3 of carbon atoms. It is described that the surfactant and low molecular weight alcohol are added to facilitate the condensed phosphate infiltrating into stains. However, though effectively infiltrating into stains, poly phosphate cannot remove intrinsic stain or heavy extrinsic stain.
U.S. Pat. Nos. 5,879,691, 5,891,453 and 5,989,569, and WO 98/55044, assigned to Procter & Gamble disclose a delivery system for a tooth whitener, comprising a transparent, thin and flexible polyethylene strip having a professional whitening gel and the like thereon, wherein the professional whitening gel and the like is pre-coated in a manufacturing process or applied directly by wearer before attaching the strip to teeth. Since it does not use a mouth tray, easiness to use is improved. Further, since the strip is thin and transparent, daily life is not interrupted when wearing the strip. However, upon reviewing the examples, it is noted that the invention of this patent is a wet type teeth-whitening system constructed by using a tooth whitening substance along with as a gelling agent, preferably carboxypolymethylene, obtained from B.F. Goodrich Company under trade name of Carbopol, water, pH adjusting agent and additive carrier materials and applying the substance onto a strip of flexible material. When handling this type of system or attaching and wearing the system onto teeth, the gel containing peroxide of a high concentration as a tooth whitener may adhere to and leave on hands, tongue, gum and the like. Therefore, there is room for improvement in handling. Further, since stabilization of peroxide in the formulation is not sufficiently assured, the whitening effect may be diminished when storing at a high temperature or for a long period of time.
WO 00/54699 discloses a strip improved in its shape over the strip of its parent patent so that a whitening agent and a strip contact with teeth in better fitting. The most important feature of this patent is that the strip is of a shape covering the user's front four teeth and two canine teeth while allowing the tips of the two canine teeth to protrude. When the strip covers the tips of the two canine teeth, it is difficult for the user to attach the strip conforming the contour of teeth so as to remain the bleaching gel in contact with the teeth surface for a sufficient time. However, when attaching a strip of a trapezoidal shape on the lower teeth and folding it over the teeth so as to attach it onto the backside of the teeth, the tongue may touch the strip, causing uncomfortable feeling. In order to improve a feeling of using the strip, it would be more desirable to provide an enough adhesion and flexibility for the system so that the system would be comfortably attached onto both the front side and the back side of the teeth than to assure a contact time by means of a shape of the system, without making the system in a trapezoidal shape or in a structure not covering the tips of two canine teeth.
U.S. Pat. Nos. 5,310,563 and 5,639,445, assigned Colgate-Palmolive Company, disclose a dental material comprising an active component dispersed in a polysiloxane polymer composition sold under the trade name Dow Corning 3179 Dilatant Compound by Dow Corning Corporation, which is attached to the teeth by pressing it against the teeth and the gum and easily removed from the teeth without breaking pieces and adhering to tooth surfaces. However, whereby the material has a construction with an active component capsulated in the polymer, the active component cannot be easily released. Consequently, it is required an extended contact time in order to obtain a tooth whitening effect.